(CNN) — Argentine footballer Emiliano Sala was exposed to high levels of carbon monoxide inside his plane before it crashed into the English Channel in January, investigators say.

Sala and pilot David Ibbotson were traveling from Nantes, France, to Cardiff, Wales, when the Piper Malibu aircraft crashed, killing them both.

Sala, 28, was traveling to make his debut with the Premier League club Cardiff City, which had signed him for a club record 17 million euros ($19 million U.S.). The plane disappeared on Jan. 21; the wreckage was found 10 days later, with Sala’s body inside.

Ibbotson’s body has still not been found, but toxicology tests on Sala’s body showed harmful levels of carbon monoxide in his blood.

A report released by the Air Accidents Investigations Branch said it was likely that Ibbotson would also have been exposed to carbon monoxide.

“Toxicology tests found that the passenger had a high saturation level of COHb (the combination product of carbon monoxide and haemoglobin). It is considered likely that the pilot would also have been exposed to carbon monoxide,” reads the report published Wednesday.

Blood tests showed Sala had a COHb saturation level of 58%. “A COHb level of 50% or above in an otherwise healthy individual is generally considered to be potentially fatal,” the report adds. Such levels could cause seizure, heart attack or loss of consciousness.

The colorless, odorless gas is produced in high concentrations in piston-engine planes, but is removed through the exhaust system.

Poor sealing of the cabin or leaks into the heating and ventilation system from the exhaust could allow the gas into a plane, according to the report.

Exposure to CO can lead to damage to the brain, heart and nervous system and, the report adds, “It is clear from the symptoms that exposure to CO can reduce or inhibit a pilot’s ability to fly an aircraft depending on the level of that exposure.”

The AAIB said it was working with the aircraft and engine manufacturers and the National Transportation Safety Board in the US to identify how the gas might have entered the cabin of an aircraft such as the Piper Malibu.

“Work is also continuing to investigate pertinent operational, technical, organizational and human factors which might have contributed to the accident,” the report concludes.